Photometric measurements are used for a variety of applications. For example, materials or systems to be measured may affect light differentially as a function of light wavelength. One major application concerns the determination of the presence and quantification of compounds in a certain liquid. In particular, in the biological and medical fields, this usually requires the measurement of light intensity after passing along an optical path through a liquid, such as blood serum, containing compounds to be determined. For most such applications, in particular those exploiting multiplexed measurements of limited sample volumes and miniaturization, there is a significant limitation on available liquid volume and hence the length of the optical path.
The above applications are based on light absorption in the liquid, and therefore signal to noise ratios are directly proportional to the optical path length.
Many applications exploit planar configurations with microfluidic setups, having large in-plane areas and small in-depth profiles. Previous work used micro-prisms and liquid routing to increase optical paths without sample volume increase. See for example. “Direct hemoglobin measurement by monolithically integrated optical beam guidance”, M. Grumann et al. TRANSDUCERS'05 pi 106-1109 (2005), incorporated herein by reference. Such devices have significant disadvantages related to manufacturability and usability.
Therefore there is a significant need for enhanced devices and methods capable of high precision photometric measurements in small liquid volumes, in particular highly multiplexed measurements, and yet being simple to manufacture and operate.